ULTRASTRUCTURE OF THE AQUEOUS LINING LAYER IN HAMSTER AIRWAYS - IS THERE A 2-PHASE SYSTEM

For particle retention and clearance, the structure and surface proper ties of the airway lining layer are important. Due to difficulties of its preservation, structural analysis has been hampered, and, hence, t he existence of two distinct and continuous phases and how much osmiop hilic material is available are unclear. It was the objective of this study to investigate the ultrastructure of the aqueous lining layer in the intrathoracic conducting airways of hamsters. By means of transmi ssion electron microscopy, we investigated the ultrastructure of the a irway lining layer in hamsters whose lungs have been fixed by the appl ication of fixative dissolved in nonpolar fluorocarbon, either by inst illation via the trachea or injection into the gas exchange parenchyma , together with intravascular perfusion of aqueous fixatives. The resu lts were compared to lungs fixed by intravascular perfusion only In tw elve hamsters, the airway lining layer was found to consist of an aque ous phase and was coated by an osmiophilic film that follows fairly cl osely the upper-extending contours of cilia protruding from epithelial cells. Substantially less osmiophilic material was preserved in extra pulmonary airways and when nonaqueous fixative was injected. We found that the aqueous lining layer of the intrathoracic airways in hamsters essentially surrounds and covers the cilia, the microvilli, and any o ther structures Like macrophages or deposited particles contained in i t and is coated by an osmiophilic film of variable thickness. In healt hy animals, a gel phase is expected to be very thin, not clearly separ ated from the periciliary fluid, and located just beneath the osmiophi lic film. (C) 1997 Wiley-Liss, Inc.